Bombs, bullets and rockets were the usual weapons on aircraft flying over Europe during the Second World War but it was often the camera that proved the most deadly. Photographs provided the generals and intelligence officers with vital information that they used to direct their forces or to out-guess the enemy.

Thousands of the photographs aircrew risked their lives to bring back are now being made publicly available for the first time. The first batch of 4,000 pictures that have remained in storage since the war go online today in a project to make up to 10 million air reconnaisance pictures available.

Images that can be seen include photographs showing the progress of the Allied invasion forces on D-Day, 6 June 1944. So detailed are the photographs that individual vehicles can be seen leaving landing-craft.

From earlier days, pictures of fields littered with the gliders, many of them wrecked, that carried many of the troops in the attempt to take Arnhem are among the collection, as are pictures of prisoners milling about in courtyards within Colditz. In photographs from the Far East can be seen the infamous bridge over the River Kwai on the Thai-Burma railway that cost so many lives. Others include some of the photographs of the Nazis' test base at Peenemunde where they developed the V-weapons, and a rare June 1945 record of a slave-labour camp near Mainz, Germany, which shortly after being pictured was razed.

"The archive shows the world at war," said Allan Williams, manager of the National Collection of Aerial Photography in Edinburgh which holds the photographs. "The skill of the photo reconnaissance pilot was incredible; they were among the best pilots in the air force. So many of them lost their lives that the archive has become a memorial to them and the events on the ground they photographed. How they could take the photos they did is astonishing when you remember they were taken in combat, and often being shot at; it's astounding."

Photographs in the archive, some of them captured from the Luftwaffe, are still used to help identify where unexploded bombs might lie, especially in Germany. Mr Williams added: "It's an archive of international significance and we are only beginning to appreciate what the archive can be used for."

When aircraft returned to base with film, the pictures were analysed by highly skilled teams of photographic interpreters with stereoscopes. Geoffrey Stone was one of them, working at RAF Medmenham, in Buckinghamshire. He said: "You have to work out what you are looking at by the clues that are around them. It could be simple things like shadows and measurements. It's rather like a detective story."

Only a fraction of the aerial war photographs survive. "People made huge bonfires after the war; we didn't think they would be needed again," said Mr Stone. "We were intoxicated by peace."

The photographs are part of the Aerial Reconnaissance Archives which contains more than 10 million images now being researched, catalogued and digitised; they were sent to Edinburgh last year from Keele University where they had been stored.